In the short term, it looks like NuBits has the advantage, because they are providing a lot more market liquidity, and holding to the peg much more tightly. NuBits is actually usable today, more so than BitUSD, because of this.

In the long term, it seems that BitUSD will outlast NuBits, because BitUSD doesn't seem to depend as much on growing demand. However, if NuBits adds a "NuBits burn" mechanism as has been discussed in their forums, which shrinks the supply of the pegged asset in exchange for creating NuShares, it could go either way.